\(n_{Na_2O}=\frac{a}{62}\left(mol\right)\)
\(PTHH:Na_2O+H_2O\rightarrow2NaOH\)
(mol) 1 1 2
(mol) \(\frac{a}{62}...............\frac{a}{31}\)
\(n_{NaOH.10\%}=\frac{m}{M}=\frac{\left(\frac{120.10}{100}\right)}{40}=0,3\left(mol\right)\)
\(\sum_{m_{NaOH}}=40.\left(\frac{a}{31}+0,3\right)=\frac{40a}{31}+12\left(g\right)\)
\(m_{ddspu}=a+120\left(g\right)\)
\(C\%_{ddNaOH}=\frac{\frac{40a}{31}+12}{a+120}.100\%=20\%\)
Giải pt ta được:
\(\Rightarrow a=11,01\left(g\right)\)